diff -r 93d3e1a8bfb0 -r 72d7d390ef5d mercurial/patch.py
--- a/mercurial/patch.py	Fri Mar 20 00:22:37 2015 +0900
+++ b/mercurial/patch.py	Thu Mar 19 10:18:05 2015 -0700
@@ -17,6 +17,7 @@
 from node import hex, short
 import cStringIO
 import base85, mdiff, scmutil, util, diffhelpers, copies, encoding, error
+import pathutil
 
 gitre = re.compile('diff --git a/(.*) b/(.*)')
 tabsplitter = re.compile(r'(\t+|[^\t]+)')
@@ -1795,8 +1796,10 @@
                eolmode='strict'):
 
     if prefix:
-        # clean up double slashes, lack of trailing slashes, etc
-        prefix = util.normpath(prefix) + '/'
+        prefix = pathutil.canonpath(backend.repo.root, backend.repo.getcwd(),
+                                    prefix)
+        if prefix != '':
+            prefix += '/'
     def pstrip(p):
         return pathtransform(p, strip - 1, prefix)[1]